Otdfbt

Everyone can think inside their head (Without producing any sound from their mouth). What is this called in English?

1. He says: "This is good." but he internally says: "This is bad".


2. He says: "This is good." but he internally thinks: "This is bad".


3. He says: "This is good." but he internally feels that this is bad.


4. He says: "This is good." but he silently thinks: "This is bad".


5. He says: "This is good." but he says: "This is bad" inside himself.


6. Something else that you would like to suggest.

I prefer the colloquial AmE. Slang is okay.

The most common term for "to think without speaking aloud" is simply "to think." However, if you want to emphasize that the person is having a private thought or a thought that contradicts his words or actions, you can use "to think to oneself," like so:

"This is good," he says, while thinking to himself that it is bad.

"This is the worst pie I've ever eaten," he thought to himself, trying his best to look as if he were enjoying it.

Internal monologue

An internal monologue, also called self-talk or inner speech, is a person's inner voice which provides a running verbal monologue of thoughts while they are conscious.

https://en.wikipedia.org/wiki/Internal_monologue

Sometimes we say a person 'keeps their thoughts to themself'. This means that they have a thought about something but they don't want others to know what their thought is.

Although he disagreed, he kept his thoughts to himself.

It usually means that the person deliberately chose not to share their thoughts, not that they just didn't bother to say anything.

We call it a lie or a fib when someone says something that they don't think is true. Usually lying is bad, but not necessarily if it is a minor lie in a social context that doesn't harm anyone (for example, telling someone that their potluck dish is good even if you didn't like it), in which case we would call it a "white lie" or a fib. It's also a common superstition to cross your fingers out of sight (behind your back or under the table) to invalidate something you say (it also can mean you are wishing for luck, so be careful!).

Here are a bunch of colloquial ways to tell your aunt that her pie was good when it wasn't:

"This is good," he lied.

"This is good," he fibbed.

"This is good," he said, while thinking the opposite.

"This is good," he said, mentally adding the word "not".

"This is good," he said, hoping she wouldn't hear the lie.

"This is good," he said, crossing his fingers under the table.

"This is good," he said, mentally crossing his fingers.

I found two derogatory words that might be suitable for this context.
One is a formal word, duplicity, which means
contradictory doubleness of thought, speech, or action

and the other one is a colloquial word. two-face,

I thought Kaila was my friend, but it turns out she talks shit about me behind my back, what a two-face.